If it's for password encryption, have you considered using
DPAPI? That can encrypt data so that only that user can decrypt it (available in Win2k+ only, though).
If you're using .Net, .Net 2.0 has built-in DPAPI support with the
ProtectedData class. If you're using .Net 1.1 Google around a bit, there's a ton of DPAPI wrappers available.